Transmitting and reflecting diffuser

ABSTRACT

An ultraviolet grade fused silica substrate is coated with vaporized fused silica. The coating thickness is controlled, one thickness causing ultraviolet light to diffuse and another thickness causing ultraviolet light to reflect a near Lambertian pattern.

X9 1 3s779i788 United S Keafer, Jr. et al.

TRANSMITTING AND REFLECTING DlFFUSER Inventors: Lloyd S. Keafer, Jr.,Yorktown;

Ernest E. Burcher; Leonard P. Kopia, both of Newport News, all of Va.

Assignee: The United States of America as represented by theAdministrator of the National Aeronautics and Space I Administration,Washington, DC.

Filed: Mar. 30, 1972 Appl. No.: 239,803

Related US. Application Data Continuation-impart of Scr. No. 38.816, May19, 1970, abandoned.

SUBSTlTUTE FOR MlSSlNG XR SEARCH ROQll 1 51 Dec. 18, 1973 ReferencesCited UNlTED STATES PATENTS 3.486870 12/1969 Vervaart et L11 A. 65/322272342 2/1942 Hyde v 65/33 1786,77) 3/1957 Long et a1. 117/46 FS3,423,324 1/1969 Best et a1. 117/106 FOREIGN PATENTS OR APPLlCATlONS587.324 11/1959 Canada 117/46 FS Primary Examiner-Alfred L. LeavittAssistant Examiner-J. Massie Attorney-John R. Manning et a1.

[57] ABSTRACT flillHFl/leletends.fused .silieasqb is Coated withvaporized fused silica. The coating thickness is controlled, onethickness causing ultraviolet light to ggg z diffuse and anotherthickness causing ultraviolet light Fie'ld 1 17/33 3 H 46 F5 to reflecta near Lambertian pattern.

1 17/62; 65/33, 32 4 Claims, 5 Drawing Figures DIFFUSER ULTRA-LAMBERT/UN VIOLET PATTERN LIGHT sounce PATENIEDUEEWW E 3.778.788

SHEET 1 [IF 2 DIFFUSER uLTRA-- LAMBERTAIN LIGHT E N SOURCE ULTRA- PRIORART v I o L E T .I-

LAMBERT/UN T SOURCE PA TERN FIG 2 REFLECTOR LAMBERTAIN PATTERN ULTRA-VIOLET LIGHT SOURCE FIG 3 INVENTORS LLOYD 5. KEAFER, JR. ERNEST E.BURCHER LEONARD F? KOPIA ATTORNEY PAIENIEBHM 3,778,788

' SHEET 2 BF 2 VAPOR DEPOSITED FUSED SILICA RELATIVE REFLECTANCEULTRAVlOLET VISIBLE WAVE LENGTH FIG. 4

INVESTORS .LLOYD S. KEAFER, JR.

ERNEST E. BURCHER LEONARD P. KOPIA BY WW1.

ATTORNEY TRANSMITTING AND REFLECTING DIFFUSER CONTlNUATlON-lN-PART Thisapplication is a continuation-in-part of application Ser. No. 38,816,filed May 19, 1970, now abandoned entitled TRANSMITTING AND REFLECTINGDIFFUSER.

ORIGIN OF THE INVENTION This invention was made by employees of theNational Aeronautics and Space Administration and may be manufacturedand used by or for the Government for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to the diffusion ofultraviolet light and relates in particular to a method of constructinga near-Lambertian diffuser for transmittance and reflectance ofultraviolet light. A Lambertian diffuser is one which diffuses a point(concentrated beam) source of reflected or transmitted light in a cosinelaw or circular pattern.

Lambertian diffusers are useful in calibrating instrumentation in thelaboratory and for use in optical equipment. The subject invention wasfirst used in the calibration of an optical radiometer.

Although opal glass serves as a near-Lambertian diffuser of visiblelight, no comparable prior art diffuser has been developed for use inthe 2,0004,000 A ultraviolet range. Absorption in the diffusing layer orscattering out the edge of the diffuser causes the diffusion pattern todeviate from Lambertian. When a thinner diffusing layer is used in anattempt to avoid absorption, a large specular or unscatterd component ofthe ultraviolet light develops causing deviation from Lambertian.

SUMMARY OF THE INVENTION The present embodiment of the invention wascon- ;structed by vaporizing and condensing ultraviolet grade j fusedsilica in a thin, even layer upon an ultraviolet grade fused silicasubstrate. The device transmitted a Accordingly, it is an object of theinvention to produce a near-Lambertian diffuser of light in the2,000-4,000 A ultraviolet range.

Another object of the invention is to produce a near Lambertian diffuserfor transmittance of ultraviolet light which gives a diffusion patternsuperior to that of opal glass in the visible range.

A further object of the invention is to produce a near- Lambertiandiffuser for reflectance of ultraviolet light which is superior to thereflectance of magnesium carbonate and magnesium oxide in theultraviolet range.

An additional object of the invention is to produce a near-Lambertiandiffuser of ultraviolet light which can be simply and cheaply producedin a variety of sizes and shapes.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of theinvention and many of the attendant advantages will be better understoodby reference to the following detailed description when considered inconnection with the accompanying drawings, wherein:

FIG. I is a schematic representation of a Lambertian transmittingdiffuser in the ultraviolet range, wherein a point (beam) source ofultraviolet light is transmitted and diffused in a circular patternvFIG. 2 is a schematic of a diffusion pattern typical of the prior artultraviolet diffuser with a high specular or non-scattered component.

FIG. 3 is a schematic representation of a Lambertian diffuser ofreflected ultraviolet light.

FIG. 4 is a graphic representation comparing the relative reflectance ofultraviolet light by the present invention with that of magnesium oxideand magnesium carbonate.

FIG. 5 is a representation of the apparatus and arrangement used toproduce the invention, a near- Lambertian diffuser of ultraviolet light.

DESCRIPTION OF THE EMBODIMENT Referring now more particularly to thedrawings, FIG. 1 is a schematic representation of a true Lambertiandiffusion of transmitted ultraviolet light. The present invention verynearly obtains this circular diffusion pattern as opposed to the priorart shown in FIG. 2.

FIG. 3 is a schematic representation of a true Lambertian diffuser ofreflected ultraviolet light. In very nearly achieving this pattern, thepresent invention has a greater relative reflectance in the ultravioletrange than standard reflectors as shown in FIG. 4.

The apparatus used in constructing the novel diffuser is shown in FIG. 5and designated generally by the ref erence numeral 10. An ultravioletgrade fused silica substrate 11 is fixed to the shaft 16 of an electricmotor I 15 by means ofa holder 13. The holder 13 is of conventionaldesign and need not be described in detail. The substrate is so heldthat the flatsurface 21 to be coated is perpendicular to the axis ofrotation and facing away from the motor 15. An ultraviolet grade fusedsilica rod 17 is mounted parallel to the surface to be coated, the axisof the rod passing through the axis of rotation of the substrate, Anoxy-acetylenc torch I9 is moved back and forth along the rod 17 at arate calculated to vaporize the fused silica rod 17 so that it isdeposited evenly upon the rotating substrate II as it condenses. Rod 17is held at a constant distance from the rotating substrate. Thisdistance is fixed according to the nozzle size and gas pressure of torch19. Although the method of vaporizing the silica red by an oxy-acetylenetorch is the preferred method of vaporization, it is to be understoodthat other means of vaporization can be utilized such asinductionheating in an inert gas and the use of an infrared laser of the CO,type.

To produce a near-Lambertian diffuser for transmit ting ultravioletlight an ultraviolet grade fused silica substrate 11 is used and thecoating thickness is kept to less than a. An optimum coating thicknesswas found to be 20 p. with greater thicknesses excessively degradingtransmittance and lesser thicknesses ad-' versely affecting difussion.At the 20 ,u. coating thickmess, the diffusion pattern of light in theultraviolet range was very nearly Lambertian. The 20 a coating thicknesshas an average specular transmittance of 0.33 percent between 2,000 and4,000 A and a totally diffuse transmittance of 1 percent in that range.The coating of the transmitting diffuser may be vitrified to increasedurability by playing the flame of torch 19 over the coating until thesurface appears slightly glassy.

To produce a near-Lambertian diffuser for reflecting ultraviolet light,any workable metal or solid material may be used as the substrate 11 andthe coating thickness is at least 100 a. The coating of the reflectingdiffuser is usually not vitrified.

The device was tested throughout the wavelength range of 2,000-4,000A. Astandard monochromator was used as the source. A photomultiplier tubehaving an 8-5 response was used in detecting the boundaries of thediffusion pattern. The detector was movably mounted so as to bepositioned within a 140 are, 70 either side of the projected ultravioletlight line. A second monochromator was used to analyze the ultravioletlight after diffusion, but no fluorescing by the diffuser was. noted. Arelative specular transmitter of 0.33 percent was measured by aspectrophotometer. Total diffuse transmittance was obtained bymultiplying this value by Tr, the diffusion pattern being very nearlyLambertian. Reflectance was also measured with a spectrophotometer forcomparison with standard reflectors in the ultraviolet range.

Slow scan, high sensitivity X-ray diffraction tests revealed that thedeposited material was non-crystalline. Electron photomicrographs of thecondensate revealed a distribution in particle size from 10 A to about10,000 A with a peak near 500 A. The excellent diffusion properties ofthe condensate are believed related to the structure of the material andparticle size.

As an alternate embodiment of this invention, it may be possible to useanother type of transmitter of ultraviolet light such as sapphire as asubstrate for the transmitting diffuser. Other combinations andmodifications are believed possible and are not to be excluded by thisteaching. lt is therefore to be'understood that within the scope oftheappended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed as new and desired to be secured by letters Patent ofthe United States is:

1, A method for the production ofa near-Lambertian transmitting diffuserof ultraviolet light comprising the step of hardening the depositedmaterial by heat treatment until the surface is slightly glassy, suchheat treatment increasing the durability of the coating.

3. The method of claim 1 whereby the step of vaporizing includestranslating heating means along the fused silica material at such a ratethat the vaporized material will be condensed evenly upon the substrate.

4. The method of claim 1 including the steps of adapting said substrateto a holding mechanism;

attaching the holding mechanism to rotational means, rotating thesubstrate;

locating the axis of rotation perpendicular to the substrate surface;and wherein the step of vaporizing ultraviolet grade fused silicamaterial includes positioning said material parallel to and at a fixeddistancefrom the substrate surface to be coated;

translating heating means along the length of the fused silica material;and the step of depositing of the vaporized material includes producinga coating thickness of 20 mircons.

a t m

2. The method of claim 1 including the additional step of hardening thedeposited material by heat treatment until the surface is slightlyglassy, such heat treatment increasing the durability of the coating. 3.The method of claim 1 whereby the step of vaporizing includestranslating heating means along the fused silica material at such a ratethat the vaporized material will be condensed evenly upon the substrate.4. The method of claim 1 including the steps of adapting said substrateto a holding mechanism; attaching the holding mechanism to rotationalmeans; rotating the substrate; locating the axis of rotationperpendicular to the substrate surface; and wherein the step ofvaporizing ultraviolet grade fused silica material includes positioningsaid material parallel to and at a fixed distance from the substratesurface to be coated; translating heating means along the length of thefused silica material; and the step of depositing of the vaporizedmaterial includes producing a coating thickness of 20 mircons.